We shall attempt more particularly here below in this document to describe the problems existing in the particular case where the system of automated distribution is used to prepare parcels. The invention is not limited of course to this particular application but is of value for any technique for processing a customer order by means of a control system for controlling a system of automated distribution having to cope with similar or proximate problems.
Parcel-preparing systems are more particularly used in firms for the dispatching and remote marketing of goods in small volumes. The main examples of users of these parcel-preparing automated systems are the suppliers of office equipment, clothing, cosmetic products, tools and spare parts in the engineering industry. These systems enable the preparation, with minimum labor, in a short time span and with precise stock tracking, of a parcel corresponding to a precise customer order from a customer, this customer order relating to different products in different quantities, each of the products with its quantity being identified by a customer order line (each customer order line therefore defines a storage container in which the desired product is situated).
One example of such an automated system for preparing parcels is described especially in the patent FR 2 915 979 filed by the present Applicant. It comprises for example:                an automated storage depot containing products in storage containers (corresponding to the above-mentioned loads), each storage container being associated with a single product reference (these can also be the containers enclosing a specific customer order and/or a mixture of products);        a customer-order preparing station where the products are picked up and placed by the operator in a parcel (a dispatch container);        a set of conveyors carrying storage containers, in which the products from the storage depot are located, to the customer-order preparing or dispatch station and vice versa; and        a warehouse control system (WCS).        
The automated storage depot comprises for example four storage units, each storage unit being formed by a lane which, on either side, serves a storage rack (or shelving unit) with several levels of superimposed storage levels, each rack being sub-divided on its length into storage locations (also called cells) each intended to receive a storage container. At each storage level, each lane receives tracks for the movement of a transfer device (also called a collecting and transportation trolley or shuttle) which shifts the storage containers so that they can be positioned within the storage locations and picked from these locations. A track is generally formed by two parallel rails and the trolley is equipped with wheels to move on these rails. The trolleys can not only move horizontally at a given storage level but also be taken from one level to another of a lane when they transport or do not transport a storage container, by means of elevators (also called up/down elevators or spiral conveyors or mini-loaders) which are laid out on either end or on both ends of the alleys (or even in the middle). These elevators furthermore enable the transfer of a storage container placed on a trolley towards the conveyor unit.
The control system manages the customer order associated with each parcel (dispatch container) and listing storage containers (loads) according to the location of the storage containers in the storage depot, the availability of the trolleys and the storage depot elevators, as well as the sequential order in which these storage containers must follow one another to the customer-order preparing station. The purpose of this is to optimize all the movements and parcel preparation time and ensure synchronization between the arrival, at the preparing station, of a parcel being prepared and of the storage containers listed in the customer order associated with this parcel being prepared.
Referring now to FIGS. 1A, 1B and 1C, we present a more detailed view of a current technique for processing a customer order by means of the control system, in the particular context (presented here above) of an automated parcel-preparing system. For the sake of simplification, not all the constituent elements of the system of automated distribution are represented in these figures.
FIG. 1A presents only:                the ends of four storage units (referenced A1 to A4) which are part of the automated storage depot and constitute four load-storing sources (storage containers);        a plurality of buffer devices (here below called source buffer devices) of the FIFO (First In First Out) type (referenced 11 to 14) and each placed immediately downstream from one of the four storage units A1 to A4 ; and        a main collector 15 (consisting for example of one or more conveyors) conveying the storage containers exiting the source buffer devices 11 to 14 up to the customer-order preparing station. The main collector 15 is therefore used to de-localize the customer-order preparing station relative to the automated storage depot. Indeed, the buildings do not always make it possible to place a customer-order preparing station beside the storage depot.        
FIG. 1C presents only:                the main collector 15;        the customer-order preparing station 16 comprising a secondary collector (formed for example by one or more conveyors) and constituting a destination receiving loads (storage containers); and        a buffer device (here below called a destination buffer device) of the FIFO-type (referenced 17), placed upstream to the customer-order preparing station 16.        
In this example, it is assumed that the customer order lists eight loads in a given sequential order corresponding to the rising sequential order of references 1 to 8 which the loads carry in the figures. In other words, the customer-order preparing station 16 must receive these eight loads in the sequential order of 1 to 8.
It is also assumed that the loads referenced 3 and 6 are stored in the storage unit referenced A1, the loads referenced 1 and 2 are stored in the storage unit referenced A2, the loads referenced 4 and 7 are stored in the storage unit referenced A3, and the loads referenced 5 and 8 are stored in the storage unit referenced A4.
To process the above-mentioned customer order, the control system carries out a first “intra-source” sequencing” (sequencing before the exit from the sources) in commanding each of the sources (storage units) A1 to A4 so that the loads of the customer order that are stored therein exit according to the given sequential order. Thus, as illustrated in FIG. 1A, the source buffer device 11 (placed downstream from the storage unit A1) successively receives the loads referenced 3 and 6. The source buffer device 12 (placed downstream relative to the storage unit A2) successively receives the loads referenced 1 and 2. The source buffer device 13 (placed downstream relative to the storage unit A3) successively receives the loads referenced 4 to 7. The source buffer device 14 (placed downstream relative to the storage unit A4 ) successively receives the loads referenced 5 and 8.
Then, the control system carries out a second “inter-source sequencing” (sequencing after the exit from the sources) in commanding the plurality of source buffer devices 11 to 14 so that the loads listed in the customer order are placed on the main collector 15 according to the given sequential order. There is therefore a high constraint of synchronization between the exits from the sources (storage units). For example, even if it is ready to exit the source buffer device 13, the load referenced 4 cannot be placed on the main collector 15 to be transmitted to the order-preparing station 16 so long as the loads referenced 1, 2 and 3 are not placed (in this sequential order) on the main collector 15.
FIG. 1B illustrates the loads referenced 1 to 8 being transported by the main collector 15 after having been placed in the desired sequential order (1 to 8).
Finally, as illustrated in FIG. 1C, the control system commands the destination buffer device 17 so that the loads (which enter therein already sorted out in the desired sequential order) can exit at the desired rate in order to be presented to the customer-order preparing station 16.
The present technique enables the simultaneous processing of several customer orders if each of them is intended for a distinct customer-order preparing station. As mentioned here above, one major drawback of the known technique illustrated in FIGS. 1A to 1C, is that there is a high constraint of synchronization between the exits of the sources (storage units). The sources therefore cannot work at a different rate and on different customer orders. Delay on the part of one source delays the others. In addition, the rate of filling of the main collector is not optimal.
Another drawback of the prior-art technique is that, when there are several destinations (preparing stations), they are not independent of each other. Indeed, when several customer orders, intended for different preparing stations, are processed simultaneously, a hitch relating to one destination (one preparing station) disturbs the other destinations. If the loads present on the main collector cannot be placed on the buffer destination device placed in front of a given destination (preparing station), then the other loads are blocked on the main collector. Similarly, a variation in the rate of one destination can block or disturb the rate of the other destinations.